1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and an apparatus of transmitting a scheduling request (SR) in a wireless communication system.
2. Related Art
Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. The wireless communication system is designed for the purpose of providing reliable communication to a plurality of users irrespective of their locations and mobility. However, a wireless channel has an abnormal characteristic such as path loss, noise, fading due to multipath, an inter-symbol interference (ISI), the Doppler effect due to mobility of a user equipment, etc. Therefore, various techniques have been developed to overcome the abnormal characteristic of the wireless channel and to increase reliability of wireless communication.
In general, the wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available radio resources. Examples of the radio resource include a time, a frequency, a code, transmit power, etc. Examples of the multiple access system include a time division multiple access (TDMA) system, a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc. The radio resource is a time in the TDMA system, a code in the CDMA system, and a subcarrier and a time in the OFDMA system.
While having almost the same complexity with the OFDMA, SC-FDMA has a lower peak-to-average power ratio (PAPR) due to a single carrier property. Since the low PAPR is advantageous for a user equipment (UE) in terms of transmission power efficiency, the SC-FDMA is adopted for uplink transmission in a 3rd generation partnership project (3GPP) long term evolution (LTE) as disclosed in section 5 of the 3GPP TS 36.211 V8.2.0 (2008-03) “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)”.
Various uplink control information are transmitted on an uplink control channel. Examples of the uplink control information include a hybrid automatic repeat request (HARQ) acknowledgement (ACK)/not-acknowledgement (NACK), a channel quality indicator (CQI) indicating downlink channel quality, a scheduling request (SR) requesting resource allocation for uplink transmission, etc.
Meanwhile, the UE transmits a sounding reference signal (SRS) to a base station (BS). The SRS is a reference signal transmitted for uplink scheduling by the UE to the BS. The BS estimates an uplink channel by using the received SRS, and uses the estimated uplink channel in the uplink scheduling.
However, if SC-FDMA is used in uplink transmission, to maintain a single carrier property, the UE cannot simultaneously transmit different signals even when using different frequency regions. This may cause ineffective use of limited radio resources.
Accordingly, there is a need for a method of transmitting an SR for the effective use of limited resources.